1. Field of the Invention
The present invention relates to a liquid droplet discharge apparatus, a piezoelectric actuator, and a method for producing the liquid droplet discharge apparatus.
2. Description of the Related Art
Conventionally, a liquid droplet discharge apparatus is known, which is constructed so that liquid droplets are discharged individually from a plurality of nozzles. For example, Japanese Patent Application Laid-open No. 2010-214795 discloses an ink-jet head which discharges liquid droplets of an ink from a plurality of nozzles respectively. The ink-jet head is provided with a flow passage unit which is formed with the plurality of nozzles and ink flow passages including, for example, a plurality of pressure chambers communicated with the plurality of nozzles respectively, and a piezoelectric actuator which discharges the ink from the corresponding nozzles by individually applying the pressure to the ink contained in the plurality of pressure chambers.
Further, the piezoelectric actuator has a vibration plate (sealing plate) which forms one wall portion of each of the plurality of pressure chambers by being joined to the flow passage unit so that the plurality of pressure chambers are covered therewith, a piezoelectric layer which is provided in a planar form on the vibration plate while ranging over the plurality of pressure chambers, and two types of electrodes (individual electrodes and common electrode) which are provided to interpose, in the thinness direction, portions of the piezoelectric layer opposed to the plurality of pressure chambers respectively. When a predetermined driving voltage is applied between the two types of electrodes corresponding to a certain pressure chamber, then the deformation (piezoelectric strain) arises in the piezoelectric layer portion interposed between the electrodes, and the vibration plate is deformed (vibrated). The volume of the pressure chamber is changed in accordance with the deformation of the vibration plate which is one wall portion of the pressure chamber. Accordingly, the pressure is applied to the ink contained in the pressure chamber, and the liquid droplets of the ink are discharged from the nozzles.
In the meantime, in the case of the liquid droplet discharge apparatus such as the ink-jet head having the plurality of nozzles as disclosed in Japanese Patent Application Laid-open No. 2010-214795, it is preferable that the discharge characteristics (amounts of liquid droplets and speeds of liquid droplets to be discharged) are evenly uniformized among the plurality of nozzles. However, actually, the discharge characteristics are different from each other among the plurality of nozzles in many cases. In the case of the exemplary ink-jet head described in Japanese Patent Application Laid-open No. 2010-214795, for example, if any difference arises in the characteristic of the piezoelectric element on account of, for example, the dispersion of the thickness of the piezoelectric layer portion (piezoelectric element) opposed to each of the plurality of pressure chambers, the deformation amount is dispersed when a predetermined driving voltage is applied. In another situation, if the constraint condition, which relates to the vibration plate and the piezoelectric layer, slightly differs among the plurality of pressure chambers, any difference also arises in the deformation amount of the vibration plate among the plurality of pressure chambers. If any difference arises in the deformation amount of the vibration plate among the plurality of pressure chambers as described above, then the pressure, which is applied to the ink, is dispersed, i.e., the liquid droplet speed and/or the liquid droplet amount is/are dispersed. Further, it is also considered that the dispersion of the discharge characteristics may be caused among the plurality of nozzles on account of any dimensional error of the ink flow passage formed in the flow passage unit including, for example, the pressure chamber and the nozzle.